accounting: use MovementHistoryListBrain.mirror_section_title directly

This compatibibility script was guessing the side, but this is exposed
in brain

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/Movement_getMirrorSectionTitle.py

-"""Retrieve the title of the mirror section
+"""Retrieve the title of the mirror section ( deprecated compatibility script )
 """
-if brain.mirror_section_uid:
-  movement = brain.getObject()
-  if brain.mirror_section_uid == movement.getDestinationSectionUid():
-    return movement.getDestinationSectionTitle()
-  return movement.getSourceSectionTitle()
+return brain.mirror_section_title